1. Field of the Invention
The invention relates to a DRAM (Dynamic Random Access Memory) of a highly integrated semiconductor device and a method of manufacturing the same, and more particularly to a DRAM having a vertical transistor whose bit line is buried in a silicon substrate and a method of manufacturing the same.
2. Related Art
Generally, the unit cell of a DRAM memory device consists of a switching transistor and a storage capacitor. As the memory device is highly integrated, the area occupied by the unit cell is reduced and thus the areas for the switching transistor and the storage capacitor must be also decreased.
Furthermore, the switching transistor is formed on the surface of the silicon substrate. In order to reduce the area of the switching transistor, the areas occupied by a source/drain and a gate of the switching transistor must be reduced. However, if areas of the source and drain are reduced, the contact process becomes difficult. Also, a serious short channel effect is produced when the gate area of the transistor is reduced. Accordingly, the area occupied by the switching transistor can be decreased only to a certain size and no more.
It is therefore an object of the present invention to provide a DRAM having a vertical transistor, which can easily reduce the area occupied by the switching transistor. The present invention accomplishes above object by providing a DRAM having a vertical transistor wherein a bit line is buried in the silicon substrate thus removing the area on the top of substrate occupied by the bit line.
Also, a word line is formed vertically on the surface of the substrate via a trench process, thereby the gate length can be elongated irrespective of the size of the unit cell thus reducing a short channel effect. Furthermore, a charge storage electrode is formed at the entrance of the trench as a stacked structure. Accordingly, on the surface of the substrate, only the charge storage electrode exists, thus, the area occupied by the charge storage electrode per unit cell can be extremely increased further unlike the conventional structure.
The preceding objects should be construed as merely presenting a few of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to both the summary of the invention and the detailed description, below, which describe the preferred embodiment in addition to the scope of the invention defined by the claims considered in conjunction with the accompanying drawings.